1. Field of the Invention
This invention relates to copper based metal alloys and more particularly to a homogeneous, ductile brazing material useful for brazing metal articles such as those composed of copper and copper alloys.
2. Description of the Prior Art
Brazing is a process for joining metal parts, often of dissimilar composition, to each other. Typically, a filler metal that has a melting point lower than that of the metal parts to be joined together is interposed between the metal parts to form an assembly. The assembly is then heated to a temperature sufficient to melt the filler metal. Upon cooling, a strong, corrosion resistant, leaktight joint is formed.
The brazing alloys suitable for use with copper and copper alloys, designated AWS BCuP are well known compositions. These alloys contain a substantial amount (about 5 to 7.5 weight percent) of the metalloid element phoshorus. Consequently, such alloys are very brittle and are available only as powder or cast rod. Powders are generally unsuitable for many brazing operations, such as dip brazing, and do not easily permit brazing of complex shapes. Although some powders are available as pastes employing organic binders, the binders form objectionable voids and residues during brazing. Rods must be melted outside the joint and, when molten, are fed into the joint by capillary action.
Some brazing alloys are available in foil form. However, such materials are either fabricated only through a costly sequence of rolling and careful heat-treating steps or are prepared by powder metallurgical techniques. Rolled foil is not sufficiently ductile to permit stamping of complex shapes therefrom. Powder metallurgical foil is not homogeneous and employs binders, which form objectionable voids and residues during brazing.
Ductile glassy metal alloys have been disclosed in U.S. Pat. No. 3,856,513, issued December 24, 1974 to H. S. Chen et al. These alloys include compositions having the formula T.sub.i X.sub.j, where T is at least one transition metal and X is an element selected from the group consisting of phosphorus, boron, carbon, aluminum, silicon, tin, germanium, indium, beryllium and antimony; "i" ranges from about 70 to about 87 atom percent and "j" ranges from about 13 to 30 atom percent. Such materials are conveniently prepared in powder, wire or foil form by rapid quenching from the melt using processing techniques that are now well-known in the art. However, no liquid-quenched glassy metal alloys of the family T.sub.i X.sub.j described above, containing copper as the principal transition metal have been reported. Chen et al. report only one copper containing composition (e.g. Pd.sub.77.5 Cu.sub.6 Si.sub.16.5) in U.S. Pat. No. 3,856,513. H. Suto and H. Ishikawa, Trans. Japan Inst. of Metals, V. 17, 1976, p. 596, report fabrication of glassy Cu-Si by vapor deposition.
There remains a need in the art for a homogeneous, copper based brazing material that is available in ductile foil form.